A LangGraph StateGraph received a non-dict return type from a node. Here’s an example: 
class State(TypedDict):
    some_key: str

def bad_node(state: State):
    # Should return a dict with a value for "some_key", not a list
    return ["whoops"]

builder = StateGraph(State)
builder.add_node(bad_node)
...

graph = builder.compile()
Invoking the above graph will result in an error like this: 
graph.invoke({ "some_key": "someval" });

InvalidUpdateError: Expected dict, got ['whoops']
For troubleshooting, visit: https://python.langchain.com/docs/troubleshooting/errors/INVALID_GRAPH_NODE_RETURN_VALUE
Nodes in your graph must return a dict containing one or more keys defined in your state.

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Troubleshooting

The following may help resolve this error:
  • If you have complex logic in your node, make sure all code paths return an appropriate dict for your defined state.